The long-term objectives of this proposal are to determine the structure and function of the nuclear lamin proteins. The nuclear lamins are Type 5 intermediate filament proteins that comprise the major structural protein of the nuclear lamina. This lamina is located at the interface between chromatin and the inner face of the inner nuclear envelope membrane. The nuclear lamins are thought to play important roles in determining the size and shape of the nucleus during interphase. They are also a major factor in regulating the disassembly of the nucleus during cell division. The specific aims of this proposal are: 1) to determine their function in the process of DNA replication; 2) to determine their role in nuclear assembly; 3) to carry out biochemical and structural analyses of the nuclear lamins; 4) to determine their dynamic properties in vivo using the green fluorescent protein; 5) to determine the mechanisms involved in the interactions between the nuclear lamins and chromatin. The methods to be used in these studies include the cloning and bacterial expression of wild-type and mutant lamins, the isolation and purification of lamins and proteins that interact with lamins, protein chemistry, high resolution electron microscopy, and a variety of cell biological methods including confocal microscopy and the production of monoclonal antibodies. The biological systems used include the Xenopus cell free nuclear assembly system, cultured mammalian cells, and the Spisula (surf clam) oocyte. Studies of the nuclear lamins and their roles in the structural organization of the nucleus are important for understanding the function of the regulation of the normal cell cycle, and chromatin organization, as well as the alterations that take place in nuclear organization in cancerous cells.